1. Field of the Invention
Embodiments of the invention are directed to nasal and oro-nasal cannulas.
2. Description of the Related Art
Related art cannulas come in several varieties. A “single lumen” cannula provides a single fluid connection from a patient's nares to a respiratory device, such as an oxygen concentrator. Each piece of tubing extending over a patient's ears fluidly merge, such as under the patient's chin or behind the patient's head. Thus, in a single lumen cannula only a single flow path exists between the patient and a respiratory device in spite of the fact that the cannula may have two nasal prongs, one for each naris. “Dual lumen,” “bifurcated” or divided nasal cannulas have to two independent flow paths, one each for each naris of a patient. Much like the single lumen cannula, a dual lumen cannula may have two nasal prongs. In a dual lumen cannula, however, the flow pathways to each naris may be separated by a barrier or bifurcation.
Nasal cannulas of any variety are a very personal item, and not generally shared with others. In fact, sharing of a nasal cannula could result in a transmission of various ailments from person to person, such as tuberculosis. The respiratory devices to which the cannulas connect may also pose a risk of transmitting various ailments. For example, a conserver device, which senses inhalation of a patient and delivers a bolus of therapeutic gas, may be transferred from patient to patient. Even if a new nasal cannula is used for each patient, the conserver may carry viruses and/or bacteria from one patient to the next. This risk is minimal for respiratory devices where patient airflow does not flow through the device.
At least some of the inventors of the present specification, however, have developed technology related to various aspects of nasal and/or oro-nasal airflow sensing where the patient's respiratory airflow, at least in part, flows through the respiratory device. For example, U.S. patent application Ser. No. 10/616,042, titled “Method and System For Measuring Air Flow of Nares” describes, in some embodiments, using mass flow sensors as the mechanism to detect nasal and/or oro-nasal respiration. U.S. patent application Ser. No. 10/697,232, titled “Method and System of Sensing Air Flow and Delivering Therapeutic Gas to a Patient” describes, in some embodiments, using mass flow sensors to sense nasal and/or oro-nasal respiration and the delivery of therapeutic gas based on those individual measurements. Finally, U.S. patent application Ser. No. 10/850,496, titled “Method and System to Determine Nasal Resistance to Air Flow” describes, in some embodiments, using mass flow sensors to determine values indicative of a patient's nasal resistance. In each of these applications, a portion of the patient's exhaled airflow passes through the nasal cannula and the respiratory device performing the measurements. Thus, if the respiratory devices are used by multiple patients, they run the risk of becoming a vehicle for the transfer of various viruses and/or bacteria. Moreover, many of the devices developed by at least some of the inventors of the present specification need to measure airflow and/or pressure of each breathing orifice individually, but these measurements are difficult using related art single lumen and/or dual lumen nasal cannulas, especially with regard to oro-nasal measurements.